Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=false, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds only that two separately-named uploads are required, which is essentially schema restatement; it says nothing about where the composited result goes, whether the original inputs are preserved, or any size/rate constraints beyond the schema's own format notes.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two tight sentences with the core action front-loaded and no filler prose. The trailing '[category: photo]' tag is minor metadata noise but the body earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For an 8-parameter non-read-only compositing tool with no output schema, the description is only minimally adequate: parameters are fully covered by the schema, but output behavior, input preservation, and sibling differentiation are absent. It is complete enough to call the tool, not complete enough to call it confidently against alternatives.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so every parameter (scale, opacity, position, offsets, formats with their units and ranges) is already documented in the schema. The description merely names the two required inputs, adding no format, defaulting, or offset-anchor detail beyond what the schema provides. Baseline 3 applies when the schema does the heavy lifting.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb ('Composite') and resource ('one image on top of another') plus the positional aspect, which is enough for an agent to identify the operation. However, it never distinguishes itself from close siblings like photo_watermark, photo_collage, or photo_meme_generator, which could all be described as overlaying imagery.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

There is no when-to-use guidance, no prerequisites, and no named alternative. The description never tells the agent when to pick this over photo_watermark or photo_collage, leaving routing entirely to inference.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.